Switch panel with touch switches

ABSTRACT

Switch panel in the form of a glass plate having markings printed thereon to form a switch space. The panel has an opaque layer on the back surface containing windows which are transparent to infrared radiation. A switch sensor responsive to infrared radiation is provided to receive any radiation that may pass through the window from an infrared radiation emitter where the radiation is reflected or dispersed when the switch space is touched.

TECHNICAL FIELD

The invention relates to a switch panel comprising a glass plate printedwith markings forming switch spaces for touch switches and switchsensors positioned behind the glass plate in the area of the switchspaces.

BACKGROUND ART

Switch panels having switch sensors for touch switches are disclosed inGerman Disclosure Document AS No. 27 55 678. In the switch panel shownin the disclosure the switch sensors are capacitive touch switchescomprising transparent touch plates positioned in front of a glass platewith which rear plates of electrically conductive material areassociated at the rear of the glass plate to form capacitors with thetouch plates which in turn are connected to a sensing circuit.

In these known switch panels, the transparent touch plates required forthe functioning of the touch switches are located in front of the glassplate in the form of thin coats or layers. These thin coats or layersare subjected to wear caused by the touching action. The layers are alsodirectly exposed to the atmosphere of the environment. In particular, ifthe moisture content of the atmosphere is high or, worse, if moistureprecipitates on the glass plates, capacity changes may occur which inturn may trigger unintended switching actions.

It is therefore a purpose of the invention to create a switch panel ofthe type described above which does not have any switch components onthe front of the panel which can be affected by wear or moisture andwhere the switching sensors will not be affected by atmosphericinfluences.

DISCLOSURE OF THE INVENTION

Broadly a switch panel constructed according to the invention comprisesa glass panel having markings pointed thereon to form switch spaces fortouch switches. Switch sensors in the form of semi-conductor elementsare located behind the glass plate in the area of the switch spaces withthe sensors being responsive to infrared radiation. An infrared emitteris provided to emit radiation through a window towards the plate wherethe window is transparent to infrared radiation. Radiation is reflectedor dispersed when the switch space is touched so that the sensors areactuated by the dispersed radiation.

According to the invention opto-electronic actuating components are usedas switching sensors which work according to the principle of electriceyes actuated by reflected light and the switching sensors are thereforecompletely insensitive to moisture. Switch panels according to theinvention are therefore particularly suited for equipment installed inrooms where the atmospheric humidity is high, such as kitchens,laundries, etc., or equipment which for other reasons is exposed tomoisture or water.

As there are no openings in the glass plate and no coatings on the frontof the glass plate which have an effect on the switching function,protection of the highest degree is ensured for the switching elementsagainst wear and/or chemical corrosion caused by components of theatmosphere.

The switch panel according to the invention may also compriseelectro-optical indicating devices which likewise do not require anyopenings in the glass plate. This permits the extension of the use ofthe switch panels according to the invention to applications whereoptical indicating devices are required or useful.

Phototransistors are suitably used as the semiconductor componentsresponding to infrared radiation. In order to reduce the sensitivity ofthe transistors against external light, a further development of theinvention provides that the windows in front of the transistors areprovided with a filter which is opaque to visible radiation, buttransparent to infrared radiation only. This filter can, for example, beapplied on the glass plate by printing.

In order to further increase protection against interference by externallight, it may be desirable to modulate the infrared emitters with shortpulses of a predetermined frequency and to design the receiving circuitso that it processes only the pulses arriving at the emitted frequency.

The necessary lettering and markings, for example those of the switchspaces, are applied to the front of the glass plate. In order to makethese visible in the dark, visible light can be introduced through theedge of the glass plate to generate a "floodlight" effect with the lightbeing dispersed by the letters and markings to partly emerge in thedirection toward the observer. According to a further development of theinvention, an emitter can be used as a light source for illuminating theedge of the glass plate which generates infrared radiationsimultaneously with the visible light so that one emitter is used forgenerating both the IR radiation used for actuating the sensors and forgenerating the visible light used for illuminating the markings.

Preferred embodiments of the invention will be described in more detailwith the aid of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section through a switch panel constructed accordingto the invention in the area of a switch space with a phototransistorand an emitting diode being used as an IR receiver and IR emitter,respectively;

FIG. 2 is a further embodiment of the panel shown in FIG. 1, in whichthe IR radiation is directed to the glass plate through an optical waveguide;

FIG. 3 is a still further embodiment of the panel shown in FIG. 1 inwhich the IR radiation enters through an edge of the glass plate; and

FIG. 4 is an example of a panel constructed according to the inventionused in an instrument panel for an automobile.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, the switch panel comprises a plate 1 of silicateglass which is preferably thermally prestressed in order to increase itsimpact and flexural strength. Markings 2 are on the side of the panelfacing an observer and comprise a frame forming a switch space on theglass plate which must be touched in order to trigger the desiredswitching operation. Markings 2 preferably comprise a white bakedvarnish.

The plate has an opaque layer 3 on its rear surface where the layer 1 isinterrupted within the switch space formed by marking 2 to form a window4 through which the infrared radiation can pass. A filtering layer 5which is opaque to visible light but which permits unimpeded passage ofIR radiation is placed within the area of window 4. A commerciallyavailable silver or yellow stain is suitable for producing a usablefiltering layer because of its special transmission characteristic.

Filtering layer 5, layer 3 which is opaque to light, and markings 2 aremade from commercially available printing colors and printed, forexample, by means of screen printing onto the cold glass plate. Afterthe printed colors have dried, they are baked onto the glass plate in aheat treating process. It is desirable to choose baking colors which arebaked at temperatures of approximately 600° C. A white ceramic bakingcolor, for example, is used for marking 2 which is sold by the DEGUSSACompany under catalog number 19710. For the opaque layer 3 on the rearsurface of the glass plate, a dull black baking color made by BLYTHECOLOURS N.V. is used, which is sold under catalog number 39 307. Forproducing the filtering layer 5, a printable silver stain, sold by theDEGUSSA Company under catalog number 73 008 is used. In order to bakethe colors onto the glass plate, the plate is heated to a prestressingtemperature and then rapidly cooled by a stream of air or anothercooling medium resulting in the glass plate being prestressed.

A receiving transistor or switch sensor 8, which is sensitive to IRradiation and an emitting diode 9 which emits IR radiation are placedside by side behind the filtering layer 5. Transistor 8 and diode 9 eachare each equipped with a small lens 10 to ensure that radiation emittedby the emitting diode is in a narrow beam and that the receivingtransistor only senses radiation arriving in a perpendicular direction.Lens 10 is arranged in such a manner that it focuses the IR radiation ofemitting diode 9 so that the focal point of the IR radiation isapproximately in the touch plane of its glass plate but in no casefurther from the plane than just above the front surface of the glass.The purpose of focusing the IR radiation is to reduce the density ofradiation outside the switch panel to such an extent that any unintendedactuation of a receiving transistor is prevented in case ofunintentional approach to the switch. The emitting and receivingdirections, respectively, of receiving transistor 8 and emitting diode 9are perpendicular to glass plate 1 and the distance between thesedevices is large enough to ensure that no coupling of the IR radiationby reflection from the filtering layer 5 or the surfaces of glass plate1 can take place. Small tubes 11, made of a material which is opaque toIR radiation, are placed around transistor 8 and diode 9 in in order toprevent direct lateral irradiation of the transistor or sensor.

In order to prevent unintended actuation of a switch sensor 8 caused byany dispersion of IR radiation emitted by the emitting diode due to themarkings 2, the markings 2 surrounding a switch space are locatedoutside the area covered by the emitting diode or the receivingtransistor. This means that the internal diameter of the markings 2 islarger than the diameter of a window 4 in opaque layer 3.

Referring to FIG. 2, a further embodiment is shown in which the switchspace is basically of the same design as the one described in FIG. 1.The switch sensor again comprises a receiving transistor 8 with anoptical lens 10 and a protective tube 11 surrounding it. However in thisembodiment, an optical wave guide 14 leading to a central IR radiationemitter is provided for bringing the IR radiation to the switch space.

The embodiment shown in FIG. 3 also includes a central IR radiationemitter. In this case, however, the IR radiation is not directed to theswitch space perpendicularly through window 4 as in the embodiments ofFIGS. 1 and 2, but enters through a lateral edge 20 of the glass plate 1from emitter 18 and from a reflector 19 placed behind the emitter. Aradiation generator is used as emitter 18 which radiates a wide spectrumof radiation and which generates visible light in addition to theinfrared light which is required for actuating the receiving transistors8. This infrared radiation is dispersed when a finger is placed on theswitching area and then sensed by the receiving transistor. The visiblelight ensures a "floodlight" illumination of markings 2 which becomevisible to the observer due to the dispersion of the light rays on theimprinted markings so that external illumination of the switch panel isunnecessary.

The IR radiation emitters, regardless of their design, are modulatedwith very short pulses, only a few microseconds long, of a givenfrequency with the result that they emit IR flashes with relatively highenergy. The receiving circuit connected to the receiving transistors isdesigned in such a way that it responds only to pulses with the emitterfrequency. This construction further contributes to the protectionagainst external light inadvertently actuating a switch sensor.

An indicating device in the shape of an electric or electronic lightsignal can be provided at the rear surface of the glass plate within thespace formed by the markings in addition to the switching sensor itselfand an IR emitter which may be required at this point. By thiscombination of switching sensor and indicating device or signal lamp, aparticularly simple and effective indication of the status of the switchis ensured.

Referring to FIG. 4, there is shown an example of a preferredapplication of a switch panel constructed according to the inventionutilized as an instrument panel for an automobile. The instrument panelcomprises several switch spaces 24 equipped with switch sensors asdescribed above and used for operating various electrical devices, suchas lights, fan, windscreen heater, radio, etc. The rectangular area 25in the switch spaces 24 depicts a window in the opaque layer behind theglass plate. A receiving transistor and a IR, not shown, are in turnlocated behind each window. Within the switch space 24 surrounded by themarkings 2, there is also provided, a smaller round window 26 locatedabove the window 25 and behind which there is placed an electrical orelectronic light signal to indicate the switch status.

For switch actions in which optical indication is not necessary, as forexample frequency and volume controls of a radio receiver, the switchspaces 28 contain merely the switch sensor. Also there may be provided anumber of circular markings 30 on the front of the glass plate withinwhich there are indicated smaller circular windows 31 in the opaquelayer on the back of the glass plate and behind which only signal lightsare positioned. These lights are independent of switch sensors and areused to indicate the status of various switches which are influenced byother switches or sensors, or for example, oil pressure and temperaturewarning lights.

I claim:
 1. Switch panel comprising a glass plate having markingsprinted on a surface thereof to form switch spaces for sensors locatedbehind the glass plate in the areas of the switch spaces, characterizedin that the switch sensors comprise semi-conductor elements responsiveto infrared radiation, in that windows transparent to infrared radiationare provided between the switch sensors and the switch spaces, in thatthe glass plate has a dull opaque layer on a rear surface thereof whichis impermeable to light, in that said windows comprise openings formedin said opaque layer, in that a filter layer comprising a printed silverstain is positioned on the rear surface of the glass plate within thearea of said windows and which is transparent to infrared radiation, andin that an emitter is provided which emits infrared radiation through awindow towards the glass plate with said radiation being reflected ordisbursed when the switch space is touched to activate the switchsensors by reflected or disbursed radiation.
 2. Switch panel accordingto claim 1 further chacterized in that the markings forming the switchspaces are printed on a front surface of the glass plate.
 3. Switchpanel according to claim 2, further characterized in that the markingscomprise a white baked enamel.
 4. Switch panel according to claim 1,further characterized in that the glass plate comprises a thermallyprestressed silicate glass and in that the markings, the opaque layerand the filter layer are baked on the glass plate during the heattreatment required for prestressing the glass plate.
 5. Switch panelaccording to claim 1, further characterized in that the switch sensorsare phototransistors which are sensitive to infrared radiation. 6.Switch panel according to claim 1, further characterized in that theemitter comprises an emitting diode which is associated with a switchsensor and which is located within the area of sensor window next to acorresponding semiconductor element.
 7. Switch panel according to claim1, including a plurality of switch sensors and further characterized inthat the emitter comprises a central IR radiation emitter with the IRradiation being brought to an appropriate sensor window by means of anoptical wave guide.
 8. Switch panel according to claim 1 including aplurality of switch sensors and further characterized in that theemitter comprises a central IR radiation emitter placed at one edge ofthe glass plate which radiates IR radiation into the glass plate andwhere the plate serves as an optical wave guide.
 9. Switch panelaccording to claims 6 or 7, further characterized in that the infraredemitter has a lens which focuses the IR radiation such that the focus islocated substantially on the front surface of the glass plate or a fewmillimeters in front of the front surface.
 10. Switch panel according toclaim 1, further characterized in that the emitter emits modulated shortpulsed, IR flashes with relatively high energy at a predeterminedemitting frequency and in having a receiving circuit controlled by theswitch sensors adopted to receive only pulses at the emitting frequency.11. Switch panel according to claim 1, further characterized in thatsaid emitter is located laterally of an edge of the glass plate andemits visible light which enters the glass plate and which is dispersedby the markings and then leaves the glass plate making the markingsvisible.
 12. Switch panel according to claim 1, further chacterized inthat said opaque layer has openings for electrooptical indicatingdevices.
 13. Switch panel according to claim 12, further characterizedin that the openings are located within the switch spaces defined by themarkings.